Power management in a wireless ad hoc network

ABSTRACT

In a wireless ad hoc network ( 20 ) of nodes ( 22 ), a method ( 64 ) of power management entails monitoring ( 82 ) a current traffic load of the network ( 20 ), and in response to the current traffic load, selecting ( 106, 132 ) a subset ( 102 ) of epochs ( 80 ) within cyclically repeating time windows ( 78 ) for network communication. A message ( 122 ) is communicated ( 120 ) between the nodes ( 22 ) in the network ( 20 ). The message ( 122 ) identifies the subset ( 102 ) of epochs ( 80 ) for using in communicating network traffic ( 32 ). Following receipt of the message, each of the nodes ( 22 ) modifies ( 124 ) a transmit capability mode by entering a run state ( 40 ) during the epochs ( 80 ) within the subset ( 102 ) to enable communication of network traffic ( 32 ) and by entering a low power consumption idle state ( 42 ) during the remaining epochs ( 80 ) within the time window ( 78 ).

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of wireless ad hoc networks.More specifically, the present invention relates to managing powerconsumption by nodes within a wireless ad hoc network.

BACKGROUND OF THE INVENTION

Over recent years, the market for wireless communications has enjoyedtremendous growth. Wireless technology now reaches or is capable ofreaching virtually every location on earth. This rapid growth inwireless communication technology and portable computing platforms hasled to significant interest in the design and development of instantlydeployable, wireless networks often referred to as “ad hoc networks” forboth military and commercial applications.

In a wireless ad hoc network, mobile user nodes are linked within alimited geographical region, and all nodes participating in the ad hocnetwork operate cooperatively to forward data packets and determinewhether the packets were successfully delivered from the original sourceto the final destination. A wireless ad hoc network has a number ofadvantages over cellular networks. For example, a wireless ad hocnetwork does not require infrastructure such as base stations or accesspoints, and it does not require any centralized administration orcontrol. As such, an ad hoc network can be entirely self-organizingbetween the mobile nodes that form the network. Thus, an ad hoc networkcan change position and shape in real time (i.e., dynamically) in orderto adapt to a changing situational environment, such as a militaryoperation, in times of emergency, such as earthquake, fire, or powerinterruption, and so forth.

In order to self-organize and operate cooperatively to forwardinformation, all wireless nodes in an ad hoc network must continuouslyprocess and forward network information (e.g., data, voice, etc). Inaddition, all nodes in an ad hoc network must continuously send andreceive routing overhead messages in order to maintain networkconnectivity. To support these operations, battery powered portablenetworking nodes in an ad hoc network continuously discharge theirbatteries. Consequently, users of such nodes are compelled to carryadditional batteries and/or to use larger batteries to maintainconnectivity to the ad hoc network for a given mission duration. Notonly is it inconvenient to carry an additional quantity of batteries, itis highly undesirable in situations where mobility, weight reduction,and an individual's load carrying capacity are fundamental to missionsuccess.

Thus, it would be desirable to have a power management scheme in awireless ad hoc network that reduces power consumption at individualwireless nodes without sacrificing network responsiveness to changes innetwork traffic activity or network capability.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be derived byreferring to the detailed description and claims when considered inconnection with the Figures, wherein like reference numbers refer tosimilar items throughout the Figures, and:

FIG. 1 shows a block diagram of an exemplary wireless ad hoc network inwhich an embodiment of the invention may be implemented;

FIG. 2 shows a state diagram for a wireless node that may be utilizedwithin the ad hoc network;

FIG. 3 shows a block diagram of a wireless node operable within thewireless network of FIG. 1;

FIG. 4 shows an exemplary time-frequency graph of communicationresources that may be accessible by wireless nodes within the wirelessad hoc network;

FIG. 5 shows a flowchart of a power management process in accordancewith another embodiment;

FIG. 6 shows an exemplary graph of a current traffic load parameterrelative to time;

FIG. 7 shows an exemplary graph of a time window indicating those epochswhich are currently available for communication of network traffic 32within the wireless ad hoc network 20;

FIG. 8 shows another exemplary graph of the time window of epochsselected for communication in response to increased network traffic;

FIG. 9 shows a graph exemplifying a timing policy in which a rapidincrease characteristic is implemented for increasing a quantity ofepochs during which network traffic may occur;

FIG. 10 shows another exemplary graph of the time window of epochsselected for communication in response to decreased network traffic;

FIG. 11 shows a graph exemplifying a timing policy in which a gradualdecrease characteristic is implemented for decreasing a quantity ofepochs during which network communication may occur; and

FIG. 12 shows yet another exemplary graph of the time window of epochsselected for communication of network traffic.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention entail methodology and a system formanaging power consumption in a wireless ad hoc network. In particular,the methodology and system extend battery life of wireless mobile nodeswithin the ad hoc network without sacrificing responsiveness or networkcapability. Power management is fundamentally achieved by identifyingand avoiding wasted power. Thus, time periods are created in which awireless node can enter a low power consumption state so that powerconsumption is effectively reduced. The reduction of wasted power inthis manner enhances the ability of the wireless mobile nodes to remainin-network performing their assigned role. By reducing wasted power,battery life can be extended. Therefore, savings is achieved in terms ofsize and weight of the wireless mobile nodes since fewer batteriesand/or smaller batteries can be used. Additionally, a reduction in powerconsumption reduces a node's thermal signature thereby increasing itsoperating life and making it less detectable to thermal imaging systems.

FIG. 1 shows a block diagram of an exemplary wireless ad hoc network 20in which an embodiment of the invention may be implemented. Exemplarywireless ad hoc network 20 includes a plurality of wireless radiodevices, referred to herein as nodes 22. Nodes 22 are configured forcommunication within wireless network 20, i.e., intra-networkcommunication, over wireless links 24. That is, wireless links 24 carrynetwork traffic as distinct bitstreams between the particular ones ofnodes 22 and others of nodes 22 within ad hoc network 20 in accordancewith particular routing solutions. Wireless links 24 may be implementedusing any suitable networking waveform, e.g., a wideband networkingwaveform (WNW), a soldier radio waveform (SRW), or another developed orupcoming networking waveform solution.

At least one of nodes 22 may additionally be configured forcommunication outside of network 20, i.e., extra-network communication.This extra-network communication is represented by a wireless channel 26between a gateway node 28 and an extra-network location, represented asa cloud element 30. Gateway node 28 provides ingress and egress into thelocal domain of nodes 22.

Ad hoc network 20 may be composed of multiple domains of nodes 22, eachdeployed in a hierarchical relationship. Nodes 22 within any domain ofad hoc network 20 can be a mixture of vehicle based and portable batterypowered nodes, and network traffic can include sensor data, voice,position data, and the like. Each of nodes 22 participates in network 20by transporting network traffic, represented by packets 32 communicatedwithin network 20 via wireless links 24. Network traffic 32 entails bothnetwork overhead traffic and user data including, for example, voice andposition information.

In certain operational scenarios, such as in a military application,nodes 22 may be lightly loaded (i.e., have a low volume of networktraffic 32) a majority of the time. However, there may be bursts ofhigher activity (i.e., a high volume of network traffic 32) interspersedwithin the given period of time. Wireless ad hoc network 20 may bedefined and organized to provide bandwidth, also referred to herein asnetwork capacity, sufficient to support the bursts of higher activity.However, these bursts of higher activity may occur occasionally. Thus,full bandwidth capacity may only be utilized infrequently. Accordingly,while it may be critical to mission success to have a given networkcapacity to support network communication, power consumption by nodes 22to maintain this capacity may be undesirably high when the networkcapacity isn't fully being utilized.

FIG. 2 shows a state diagram 34 for a wireless node 22 that may beutilized within the ad hoc network 20. A number of strategies have beendeveloped to reduce power consumption at wireless nodes 22 byperiodically placing nodes 22 in a lower power mode, such as an idlestate or a sleep state. By way of example, as illustrated in FIG. 2,each of nodes 22 may be capable of functioning in either of twofundamental modes. These two fundamental modes can be an operationalmode 36 and a sleep mode 38. In operational mode 36, node 22 is capableof operation within network 20 in which network traffic 32 (FIG. 1) canbe passed between nodes 22.

In an exemplary scenario, operational mode 36 can include a run state 40and an idle state 42, where run state 40 can further be subdivided intoa transmit state 44 and a receive state 46. When node 22 enters idlestate 42, it neither receives nor transmits network traffic 32 (e.g.,overhead messages or user data). Whereas, when node 22 enters run state40, it is instantaneously capable of receiving and/or transmittingnetwork traffic 32. Power consumption by node 22 in idle state 42 istypically much lower than when node 22 is in run state 40 since node 22neither receives nor transmits network traffic 32 in idle state 42.

Like idle state 42, sleep mode 38 also refers to a low power consumptionmode for node 22. However, in sleep mode 38, certain elements (e.g.,oscillator, voltage regulator, transceiver, etc.) of node 22 may beturned off so that node 22 enters a sleep state 47 in order to minimizepower consumption. Accordingly, power consumption by node 22 in sleepmode 38 can be significantly less than power consumption by node 22 inidle state 42.

Aside from power consumption, a notable difference between idle state 42and sleep mode 38 is that of latency, i.e., the time delay experiencedby node 22 to either enter or exit run state 40. In wireless ad hocnetwork 20, this time delay can affect whether node 22 remains“in-network” (i.e., is recognized as a member of ad hoc network 20) orwhether node 22 becomes “extra-network” (i.e. node 22 is no longerrecognized as a member of ad hoc network 20).

In idle state 42, node 22 is neither transmitting nor receiving, butsince multiple elements of node 22 are not powered down in idle state42, an interrupt can result in transition from idle state 42 to runstate 38 with a very short transition delay. Thus, in idle state 42,node 22 can maintain network connectivity with the remainder of nodes 22in ad hoc network 20. That is, node 22 in idle state 42 can remain“in-network,” and will be recognized as such by the remainder of nodes22.

In contrast, when node 22 is in sleep mode 38, node 22 may lose networkconnectivity with remaining nodes 22 in ad hoc network 20. A transitionfrom sleep state 47 to run state 40 may occur as a result of a realtimeclock alarm, i.e., a search wakeup alarm 48. In response to searchwakeup alarm 48, node 22 may be compelled to enter a search state 50 topower up various components that were powered down and to send overheadmessages in order to reestablish network connectivity with nodes 22 ofad hoc network 20. Consequently, the transition from sleep mode 38 torun state 40 can be many times longer than the transition from idlestate 42 to run state 40.

Typical networking waveforms use a time slotted structure of, forexample, Time Domain Multiple Access (TDMA) and/or Carrier SenseMultiple Access (CSMA). Such a scheme allows each node 22 within ad hocnetwork 20 a great deal of flexibility to access the radiofrequency (RF)medium, i.e. wireless links 24 (FIG. 1), during the time slots. Timeslot access is generally available on a scheduled basis or a contentionaccess basis, such as CSMA. The unpredictability of contention basedaccess to wireless links 24 makes power management particularchallenging. Power management is difficult because all nodes 22 withinnetwork 20 need to constantly “listen” for network traffic in order toallow the network traffic to be sent on any time slot with little or noa-priori knowledge. As such, wireless network nodes 22 must continuallybe in receive state 46 during mission critical time periods, therebyconsuming power. Moreover nodes 22 must be in receive state 46, evenwhen nodes 22 are not currently receiving or transmitting networktraffic 32 (FIG. 1).

In addition, all nodes 22 within wireless ad hoc network 20 continuallyparticipate in the network overhead that maintains connectivity amongthese dynamic, physically moving network nodes 22. As nodes 22 moveabout, they exchange messages with each of their neighboring nodes 22 totrack the most favorable wireless links 24 in order to maintain constantcontact to their local neighbor nodes 22. Likewise, these local wirelesslinks 24 allow network 20 to compute routing solutions between allneighboring nodes 22 and gateway nodes 28 which provide ingress andegress to the local domain of the wireless ad hoc network 20. Theconstant requirement to participate in maintaining the network routingsolution further complicates power management because the individualnodes 22 need to continually be in run state 40 (FIG. 2) in order tosend and receive overhead messages.

Consequently, it is undesirable and impractical for nodes 22 to entersleep mode 38 during mission critical periods due at least in part toloss of network connectivity and undesirably long latencies to wake up,reestablish connectivity, and enter run state 40. Conversely, it is alsoundesirable to remain constantly in run state 40 due to excessive powerconsumption concerns.

As discussed in detail below, embodiments of the invention fundamentallyachieve efficient power management by creating more periods of time fornodes 22 to be in idle state 42 so as to reduce power consumption atnodes 22. By reducing power consumption, battery life can be extendedthereby resulting in a reduction in size and weight of wireless mobilenodes 22, due to a reduction in a quantity or physical size of thebatteries needed to power nodes 22. However, by creating more time thatnodes 22 are in idle state 42 (as opposed to sleep state 47), nodes 22can remain in-network performing their role. Moreover, nodes 22 canrapidly transition to run state 40 as traffic load in ad hoc network 20dictates.

FIG. 3 shows a block diagram of one of wireless nodes 22 (FIG. 1)operable within wireless ad hoc network 20 (FIG. 1). Node 22 may be asoftware definable radio system that includes, for example, atransceiver 52 configured for intra-network communication over wirelesslink 24. A processor section 54 is in communication with transceiver 52and a computer-readable storage medium 56. Likewise, processor section54 may be in communication with an input section 58 (e.g., keypad,touchscreen, microphone, sensor, and the like) and a display 60.

Computer-readable storage medium 56 may contain communication algorithms62 executable by processor 54 that define channel modulation waveforms;modulation techniques; wideband analog-to-digital and digital-to-analogconversion; the implementation of intermediate frequency, baseband, andbitstream processing functions; and so forth. Through the execution ofcommunication algorithms 62, processor 54 controls the transfer ofsignals, i.e., network traffic 32, to and from node 22. That is,processor 54 enables forwarding of network traffic 32 as distinctbitstreams over wireless links 24 between node 22 and one or more othernodes 22 of wireless ad hoc network 20.

In accordance with an embodiment, computer-readable storage medium 56further contains a power management algorithm 64 executable by processor54. Processor 54 executes power management algorithm 64, referred tohereinafter as a power management process 64, to control when thetransfer of signals, i.e., network traffic 32, to and from node 22 willtake place. More particularly, through the execution of power managementprocess 64, processor 54 dynamically scales the needed bandwidth ofwireless links 24 in accordance with a current traffic load of wirelessad hoc network 20. This scaling of bandwidth is accomplished in order tocreate more periods of time that node 22 is in the lower powerconsumption idle state 42 (FIG. 2), while rapidly increasing thebandwidth as the network traffic load and/or network mobility dictates.

FIG. 4 shows an exemplary time-frequency graph 66 of communicationresources 68 that may be accessible by wireless nodes 22 and utilizedwithin wireless ad hoc network 20 (FIG. 1). In this exemplaryembodiment, communication resources 68 may include multiple frequencychannels 70 which may be utilized for control, data, and voicetransmission in accordance with known and developing networking waveformmethodologies.

In some embodiments, frequency channels 70 may be divided into fixedintervals in time, known as frames 72, illustrated in conjunction withone of frequency channels 70. Frames 72 may be divided into one or moretimeslots 74 (illustrated in conjunction with one of frames 72) inaccordance with a particular time slotted structure implemented withinthe networking waveform technique for wireless ad hoc network 20.Timeslots 74, each of which accommodates a single burst of information,may be utilized for network traffic 32 (FIG. 1), such as overheadmessages and/or user data.

Network traffic 32 may include network access data, configurationinformation of timeslots 74, forwarding acknowledgements, usercommunications from nodes 22, such as voice, status information,position data, sensor data, and so forth.

A horizontal x-axis 76 of time-frequency graph 66 provided in FIG. 4represents time divided into successive cyclically repeating timewindows 78. For example, time window 78 repeats each second. Typically,networks, such as wireless ad hoc network 20 (FIG. 1), break up thesetime windows 78 in shorter blocks of time referred to as epochs 80. Inthis example, each of time windows 78 is one second in duration, andthere are ten epochs 80 in each time window 78. Network 20 communicatesnetwork traffic 32 (FIG. 1) using timeslots 74 within frequency channels70 during time periods defined by epochs 80. Although time-frequencygraph 66 shows each of the one second time windows 78 being divided intoten epochs, it should be understood that there may be a different numberof epochs 80 per time window 78 (for example, one hundred epochs persecond).

When ad hoc network 20 is fully loaded, network traffic 32 iscommunicated via frequency channels 70 during all epochs 80, thusproviding one hundred percent network capacity, or bandwidth. Bandwidthrefers to the maximum amount of information (e.g., bits/second) that canbe transmitted via communication resources 68). However, when ad hocnetwork 20 is lightly loaded, communication of network traffic 32 withinnetwork 20 may take place during only a few epochs 80 per second.Indeed, when ad hoc network 20 is very lightly loaded, ninety toninety-nine percent of the time, subdivided into epochs 80, no networkcommunication may take place. That is, frequency channels 70 may beunused. Accordingly, in time of reduced network activity,correspondingly reduced network capacity, or bandwidth, may be used.

Network traffic 32 is communicated within ad hoc network 20 viafrequency channels 70. However, in accordance with the execution ofpower management process 64 (FIG. 3), network traffic 32 is communicatedvia frequency channels 70 over established wireless links 24 (FIG. 1)during specified predetermined periods of time, i.e., during a subset ofepochs 80 within each successive time window 78. Any remaining unusedepochs 80 within time window 78 can then be made available for powersavings, discussed below.

Referring now to FIG. 5, FIG. 5 shows a flowchart of power managementprocess 64. Power management process 64 is executed to determine acurrent traffic load of wireless ad hoc network 20 (FIG. 1) and toselect a subset of epochs 80 within successive time windows 78 duringwhich network traffic 32 may be communicated via frequency channels 70.As such, network capacity, i.e., the bandwidth, can be increased ordecreased to accommodate the current traffic load of network 20.

The power management function of process 64 may be implemented in acentralized manner or in a more distributed manner. For example, in acentralized implementation, power management process 64 may be executedby only one of nodes 22 serving as a network manager. The networkmanager node 22 responds to conditions of changing traffic loads bysending out a message to all other nodes 22 in network 20 to change thenumber of active epochs 80 (FIG. 4). The terms “active epoch” or “activeepochs” used herein refers to those epochs 80 during which networktraffic 32 (FIG. 1) may be communicated. Conversely, “inactive epoch” or“inactive epochs” refers to the remaining epochs 80 within time window78 during which network traffic 32 is not communicated. These inactiveepochs 80 are time periods during which power savings techniques may beimplemented.

In a distributed implementation, power management process 64 may beexecuted by each of nodes 22. Coordination of epoch adjustment may beperformed as a voting action among nodes 22. Decisions regarding achange in the number of active epochs 80 may call for unanimous consent,near unanimous consent, or consent within domains, islands, or subnetsof nodes 22. For simplicity of description, power management process 64will be discussed in connection with its execution at one of nodes 22within ad hoc network 20. However, the generalized operations of powermanagement process 64 apply equivalently to both of the centralized anddistributed implementation scenarios mentioned above.

Power management process 64 begins with a task 82. At task 82, node 22monitors a current traffic load of wireless ad hoc network 20. Thecurrent traffic load may be monitored by acquiring knowledge, throughmessaging, of queue utilization of network traffic 32 (FIG. 1) atvarious nodes 22. For example, queue analysis may include queue filldepth versus time.

In addition, to queue analysis, the monitoring of the current trafficload and traffic load analysis may further take into account quality ofservice considerations (QOS) and/or network mobility. Regarding QOSconsiderations, the adjustment of a quantity of epochs 80 (FIG. 4) forcommunicating network traffic 32 can take into account the priority ofnetwork traffic 32 so as to optimize the quantity of epochs 80 used forcommunicating network traffic 32 when high priority network traffic 32or network traffic 32 sensitive to latency is to be communicated.Latency sensitive network traffic 32 includes, for example, voicetraffic. Lower priority network traffic 32 as represented, for example,in an IP packet QOS marking, can tolerate higher latencies and thelonger queuing time that could result when a quantity of epochs 80available for communicating network traffic 32 is reduced.

Regarding network mobility, the adjustment of a quantity of epochs 80(FIG. 4) for communicating network traffic 32 can also take into accountknowledge of the mobility of nodes 22 within wireless ad hoc network 20(FIG. 1). When network traffic 32 demand is moderate or low, and nodes22 are geographically immobile, the quantity of epochs 80 available forcommunicating network traffic 32 can be maintained low or can be reducedbecause the need for network topology adjustments is reduced. As nodes22 begin to geographically move about, their rate of movement canincrease the need for more frequent network maintenance. This rate ofchange may be used within traffic load analysis of task 82 to influencean increase in the quantity of epochs 80 available for communicatingnetwork traffic 32.

A query task 84 is performed in connection with task 82. At query task84, a determination is made as to whether the traffic load analysisperformed at task 82 indicates that the current traffic load exceeds ahigh traffic load threshold.

Referring to FIGS. 6 and 7 in connection with task 84, FIG. 6 shows anexemplary graph 86 of a current traffic load parameter 88 relative totime 90, and FIG. 7 shows an exemplary graph 92 of time window 78indicating those epochs 80 which are currently available forcommunication of network traffic 32 (FIG. 1) within wireless ad hocnetwork 20 (FIG. 1).

In response to traffic load monitoring and analysis at task 82 (FIG. 5),current traffic load parameter 88 represents the current traffic loadwithin network 20, and taking into account quality of serviceconsiderations and network mobility. At a first instant in time 94,labeled T1, traffic load parameter 88 falls within a traffic load window96 delineated by a high traffic load threshold 98 and a low traffic loadthreshold 100.

At first instant in time 94, node 22 may have selected two of epochs 80to be a subset 102 of epochs 80 during which network traffic 32 (FIG. 1)is to be communicated via wireless links 24 (FIG. 1) using frequencychannels 70 (FIG. 7). That is, subset 102 defines a duration withinsuccessive time windows 78 during which nodes 22 within wireless ad hocnetwork 20 are in run state 40. Nodes 22 may enter the lower powerconsumption idle state 42 during the remaining epochs 80 within timewindow 78, in which nodes 22 abstain from communicating network traffic32.

Thus, power savings is achieved in the example shown in FIG. 7 byplacing nodes 22 in idle state 42 approximately eighty percent of theduration of time window 78. Time window 78 is one of cyclicallyrepeating time windows, as illustrated in FIG. 4. Accordingly, the samesubset 102 of epochs 80 will remain available for communication ofnetwork traffic 32 until the quantity of epochs 80 per time window 78are increased or decreased in accordance with the execution of powermanagement process 64. Although one power savings technique isrepresented by placing nodes 22 in idle state 42, different oradditional power savings techniques may alternatively be implemented.

At query task 84 (FIG. 5), at a second instant in time 104, labeled T2,a determination is made that current traffic load parameter 88 exceedshigh traffic threshold window 98. Accordingly, power management process64 proceeds to a task 106.

At task 106, subset 102 of epochs 80 is adjusted or otherwise selectedto accommodate the increasing traffic load. That is, a quantity ofepochs 80 (FIG. 4) per successive time windows 78 (FIG. 4) that areavailable for communicating network traffic 32 is increased.

Referring to FIG. 8 in connection with task 106, FIG. 8 shows anotherexemplary graph 108 of time window 78 of epochs 80 selected forcommunication in response to increased network traffic 32. In responseto task 106, a second subset 110 of epochs 80 within time window 78 isformed in response to current traffic load parameter 88 (FIG. 6) atsecond instant in time 104 (FIG. 6). In this example, second subset 110of epochs 80 includes all epochs 80 within time window 78, andsuccessive ones of the cyclically repeating time windows 78. Sincecommunication of network traffic 32 can occur during all epochs 80,wireless ad hoc network 20 can utilize one hundred percent of itsnetwork capacity, i.e., bandwidth. However, during the time whencommunication can occur during all epochs 80, as specified in secondsubset 110, nodes 22 will not enter idle state 42 (FIG. 2) and no powersavings will be achieved.

With reference back to power management process 64 (FIG. 5), a task 112is performed in connection with task 106. At task 112, node 22 sets atiming policy for increasing the quantity of epochs 80 from first subset102 (FIG. 7) to second subset 110 (FIG. 8) of epochs 80. In anembodiment, the rate of increase in epochs 80 to second subset 110 canbe tailored for each implementation. By way of example, in criticalapplications, responding to an increased traffic load may require thatnetwork 20 return to one hundred percent capacity as rapidly possible.

Referring to FIG. 9 in connection with task 112, FIG. 9 shows a graph114 exemplifying a timing policy 116 in which a rapid increasecharacteristic 118 is implemented for increasing a quantity of epochs 80during which network traffic 32 may occur. As shown, timing policy 116entails an aggressive recovery policy to enable network communicationduring second subset 110 (FIG. 8) of epochs 80 (FIG. 8) as quickly aspossible. In this exemplary instance, the adjustment from two epochs 80per second, as specified in first subset 102 (FIG. 7) of epochs 80, toall ten epochs 80 per second, as specified in second subset 110 (FIG. 8)of epochs 80 should be enabled in less than one second.

With reference back to power management process 64 (FIG. 5), followingthe execution of tasks 106 and 112, process 64 continues with a task120.

At task 120, node 22 communicates management messages 122 as networktraffic 32 to all nodes 22 within wireless ad hoc network 20. Managementmessages 122 can provide nodes 22 with information regarding secondsubset 110 (FIG. 8) of epochs 80, such as quantity of epochs 80 and theparticular epochs (80), as well as timing policy 116 (FIG. 9).

Process 64 continues with a task 124. Following receipt of managementmessages 122, each of nodes 22 modifies its transmit capability mode byentering run state 40 (FIG. 2) to enable network communication duringepochs 80 within the adjusted subset of epochs (e.g., second subset 110illustrated in FIG. 8) and by entering a non-communication state, suchas idle state 42 (FIG. 2) during the remaining ones of epochs 80 (ifthere are any) within the cyclically repeating time window 78.

Following task 124, power management process 64 continues with a querytask 126. At query task 126, a determination is made as to whether powermanagement process 64 is to continue. Process 64 may continue for anentire duration of a mission operation being carried out by members ofwireless ad hoc network 20 (FIG. 1), and may end following thatparticular mission operation. Under such a circumstance, following aparticular mission operation, when a determination is made at query task126 that the execution of process 64 is to be discontinued, process 64ends. Alternatively, when a determination is made at query task 126 thatthe execution of process 64 is to continue, program control loops backto task 82 to continue monitoring the current traffic load, and increaseor decrease epochs 80 available for network communication in response tothe current traffic load for network 20.

As discussed above, tasks 106, 112, 120, and 124 are performed whencurrent traffic load parameter 88 (FIG. 6) is greater than high trafficload threshold 98 so as to increase a quantity of epochs 80 during whichnetwork communication can take place. However, referring back to querytask 84 of process 64, when a determination is made that current trafficload parameter (FIG. 6) is not greater than high traffic load threshold98 (FIG. 6), process 64 continues with a query task 128.

At query task 128, a determination is made as to whether the trafficload analysis performed at task 82 indicates that the current trafficload is less than a low traffic load threshold.

Referring back to FIG. 6, following second instant in time 104 and theadjustment of transmit capability to second subset 110 of epochs 80,traffic load window 96 has shifted so that high and low trafficthresholds 98 and 100, respectively, are commensurately shifted. At athird instant in time 130, labeled T3, current traffic load parameter 88is now less than this reset low traffic load threshold 96. When currenttraffic load parameter 88 is less than low traffic load threshold 96,power management process 64 continues with a task 132.

At task 132, subset 110 (FIG. 8) of epochs 80 is adjusted to accommodatethe decreasing traffic load. That is, a quantity of epochs 80 (FIG. 4)per successive time windows 78 (FIG. 4) that are available forcommunicating network traffic 32 is decreased.

Referring to FIG. 10 in connection with task 132, FIG. 10 shows anotherexemplary graph 134 of time window 78 of epochs 80 selected forcommunication in response to decreased network traffic 32.

In response to task 132, a third subset 136 of epochs 80 within timewindow 78 is formed in response to current traffic load parameter 88(FIG. 6) at third instant in time 130 (FIG. 6). In this example, thirdsubset 136 of epochs 80 includes only one epoch 80 within time window 78and successive ones of the cyclically repeating time windows 78. Sincecommunication of network traffic 32 can occur only during one epoch 80per time window 78, ninety percent of the duration of time window 78(i.e., nine epochs per second) is available for power savingstechniques.

As shown in graph 134, ad hoc network 20 (FIG. 1) is lightly loaded.That is, there is only minimal network traffic 32 currently beingcommunicated via wireless links 24 (FIG. 1). In this example, thissingle epoch 80 within third subset 136 is available for networkcommunication that includes, at least, overhead messaging and bandwidthmanagement messages 122. In an embodiment, the same epoch 80 in eachtime window 78 (FIG. 4), i.e., the same period of time, may be availablefor network communication to carry overhead messages, bandwidthmanagement messages 122, and the like in order to maintain nodes(FIG. 1) in-network and to maintain, or establish, routing solutions.

With reference back to power management process 64 (FIG. 5), a task 138is performed in connection with task 132. At task 138, node 22 sets atiming policy for decreasing the quantity of epochs 80 from, forexample, second subset 110 (FIG. 8) to third subset 136 (FIG. 10) ofepochs 80. That is, the rate of decrease of epochs 80 to the singleepoch 80 of third subset 136 can be tailored for each implementation.For example, response to a decreased traffic load may occur gradually.

Referring to FIG. 11 in connection with task 138, FIG. 11 shows a graph140 exemplifying a timing policy 142 in which a gradual decreasecharacteristic 144 is implemented for decreasing a quantity of epochs 80during which network traffic 32 may occur. As shown, timing policy 142entails a gradual decay policy to enable network communication duringepochs 80 within third subset 136 (FIG. 10) of epochs 80 (FIG. 8). Inthis exemplary instance, the adjustment from ten epochs 80 per second,as specified in second subset 110 (FIG. 8) of epochs 80, to only oneepoch 80 per second, as specified in third subset 136 (FIG. 10) ofepochs 80 can be enabled in approximately five seconds.

It should be understood that graph 114 (FIG. 9) and graph 140 (FIG. 11)show only two, of many, possible responses to increased network traffic32 and/or decreased network traffic 32). Those skilled in the art willrecognize that a particular timing policy for increasing and/ordecreasing epochs 80 available for network communication can be variedin accordance with particular wireless ad hoc network implementationstaking into account, for example, the criticality of communication,quality of service considerations, latency, network mobility, and soforth.

Returning to power management process 64 (FIG. 5), following task 138,program control continues with tasks 120 and 124 in which bandwidthmanagement messages 122 are communicated to all nodes 22 within wirelessad hoc network 20 with information regarding third subset 134 (FIG. 10)of epochs 80, followed by each node 22 modifying its transmit capabilityin accordance with third subset 136. Subsequent to the execution oftasks 120 and 124, continuation query task 126 may be performed, asdiscussed above.

Now returning to query tasks 84 and 128, when a determination is made atquery task 84 that the current traffic load is not greater than hightraffic load threshold 98 (FIG. 6) and a determination is made at querytask 128 that the current traffic load is not less than low traffic loadthreshold 100 (FIG. 6), power management process 64 continues with atask 146. At task 146, the current subset of epochs 80 available fornetwork communication is maintained unchanged. That is, negativeresponses to each of tasks 84 and 128 indicates that the current trafficload, represented by current traffic load parameter 88 (FIG. 6), fallswithin traffic load window 96 supportable by the subset of epochs 80available for network communication. Therefore, the quantity of epochs80 within time window 78 (FIG. 4) that are available for networkcommunication need not change.

Following task 146, process 64 may simply proceed to continuation task126, as discussed above. In addition, or alternatively, as illustratedin FIG. 5, tasks 120 and 124 may be performed, as needed, to communicatemanagement messages 122 regarding the current subset of epochs 80 (e.g.,first subset 102 (FIG. 7) available for network communication so thateach of nodes 122 can verify that its transmit capability has beenmodified in accordance with the appropriate subset of epochs specifiedin management messages 122. Subsequently, continuation query task 126may be performed as discussed above.

FIG. 12 shows yet another exemplary graph 148 of time window 78 ofepochs 80 selected for communication of network traffic 32 (FIG. 1). Asshown in graph 148, epochs 80 selected for inclusion in a subset 150 ofepochs 80 are approximately uniformly distributed within time window 78.

Under some conditions, all epochs 80 within each time window 78 need notbe selected to support network traffic 32. That is, full bandwidth isnot required. However, quality of service (QOS) characteristics ofnetwork traffic 32 may call for reduced latency. Through an appropriateselection of epochs to form subset 150, latency can be kept short whilestill making some epochs 80 available for power savings.

Conversely, graph 92 (FIG. 7) illustrates a condition in whichimmediately adjacent epochs 80 within time window 78 are selected forinclusion in subset 102 (FIG. 7). Such a condition is advantageous forpower savings in that elements within nodes 22 can power up, i.e.,become active, in order to enter run state 40 (FIG. 2) and stay activeuntil no longer needed during each time window 78, thereby reducing thenumber of power up and power down cycles.

Consequently, epochs 80 within subset 150 are selected to minimizelatency with some sacrifice in power savings. Whereas, epochs 80 withinsubset 102 are selected to maximize power savings with some adverseimpact to the latency characteristics. Thus, it should be apparent thatvarious epoch selection schemes may be implemented in accordance withparticular wireless ad hoc network implementations taking into account,for example, the tradeoff between power savings and latency.

In summary, the present invention entails methodology and a system formanaging power consumption in a wireless ad hoc network by dynamicallyvarying network capacity in favor of using less power in response todemand. In particular, a power management scheme is implemented in whichtime periods are formed during which a network node can enter a lowpower, non-communication state. These time periods are formed based oncurrent traffic loads, and these time periods can rapidly change as aresult of network traffic or mobility demands. The time spent in theselower power states can vary from one epoch in ten to as many as nineepochs in ten. This allows the network nodes to be in a lower powerconsumption state ten to ninety percent of the time. However, since thenodes are still sending and receiving network routing overhead messagesat least one epoch per second, the nodes remain in-network and do nothave to reacquire the network when network traffic increases. Thisavoids a significant time penalty as compared to power managementtechniques where a node leaves the network for periods of time.

The reduction of wasted power enhances the ability of the wirelessmobile nodes to remain in-network performing their assigned role. Byreducing wasted power, battery life can be extended. Therefore, savingsis achieved in terms of size and weight of the wireless mobile nodessince less batteries and/or smaller batteries can be used. Additionally,a reduction in power consumption reduces a node's thermal signaturethereby increasing its operating life and making it less detectable tothermal imaging systems.

Although the preferred embodiments of the invention have beenillustrated and described in detail, it will be readily apparent tothose skilled in the art that various modifications may be made thereinwithout departing from the spirit of the invention or from the scope ofthe appended claims. For example, the order of tasks can be variedgreatly from that which was presented. In addition, the particularbandwidth management messages can be varied in accordance with thecharacteristics of a particular wireless ad hoc network.

1. A method of power management in a wireless ad hoc network, saidnetwork including a plurality of nodes, and said method comprising:monitoring a current traffic load of said wireless ad hoc network; inresponse to said current traffic load, selecting a subset of epochswithin a time window of epochs for network communication; communicatinga message between said nodes in said network, said message identifyingsaid subset of epochs as being allowable for use in communicatingnetwork traffic; and following receipt of said message, said each ofsaid nodes modifying a transmit capability mode by entering a run stateto enable communication of said network traffic over said network duringsaid epochs within said subset of epochs and by entering an idle stateduring remaining ones of said epochs within said time window.
 2. Amethod as claimed in claim 1 wherein said time window is one ofcyclically repeated time windows, each of said cyclically repeated timewindows comprising said epochs, and said method further comprises:communicating said network traffic during said epochs within said subsetof epochs for said each of said cyclically repeated time windows; andabstaining from communicating said network traffic during said each ofsaid cyclically repeated time windows when said each of said nodes is insaid idle state.
 3. A method as claimed in claim 1 wherein said currenttraffic load is a first traffic load determined at a first instant intime, said subset of epochs is a first subset of epochs, and said methodfurther comprises: detecting a second current traffic load at a secondinstant in time following said first instant in time; adjusting saidfirst subset of epochs to form a second subset of epochs within saidtime window in response to said second current traffic load;communicating a second message between said nodes in said network, saidsecond message identifying said second subset of epochs as beingallowable for use in communicating said network traffic; and followingreceipt of said second message, said each of said nodes modifying saidtransmit capability mode by entering said run state to enablecommunication of said network traffic during said epochs within saidsecond subset of epochs and by entering said idle state during saidremaining ones of said epochs within said time window.
 4. A method asclaimed in claim 3 further comprising comparing said second currenttraffic load with one of a high traffic load threshold and a low trafficload threshold; said adjusting operation increases a second quantity ofsaid epochs within said second subset of epochs relative to a firstquantity of said epochs within said first subset of epochs when saidsecond current traffic load is greater than said high traffic loadthreshold; and said adjusting operation decreases said second quantityof said epochs within said second subset of epochs relative to saidfirst quantity of said epochs within said first subset of epochs whensaid second current traffic load is less than said low traffic loadthreshold.
 5. A method as claimed in claim 4 further comprising:detecting a mobility characteristic for said each of said nodes, saidmobility characteristic being one of a substantially staticcharacteristic and a mobile characteristic; said adjusting operationincreases said second quantity of said epochs within said second subsetof epochs when said second current traffic load is greater than saidhigh traffic load threshold and said mobility characteristic for atleast some of said nodes is said mobile characteristic; and saidadjusting operation decreases said second quantity of said epochs withinsaid second subset of epochs when said second current traffic load isless than said low traffic load threshold and said mobilitycharacteristic for said at least some of said nodes is saidsubstantially static characteristic.
 6. A method as claimed in claim 3wherein: said adjusting operation increases a second quantity of saidepochs of within said second subset of epochs relative to a firstquantity of said epochs within said first subset of epochs; and saidmodifying operation modifies said transmit capability mode in accordancewith an aggressive recovery policy, said aggressive recovery policyenabling said network communication during said second subset of epochsin accordance with a rapid increase characteristic of said aggressiverecovery policy.
 7. A method as claimed in claim 3 wherein: saidadjusting operation decreases a second quantity of said epochs withinsaid second subset of epochs relative to a first quantity of said epochswithin said first subset of epochs; and said modifying operationmodifies said transmit capability mode in accordance with a gradualdecay policy, said gradual decay policy enabling said networkcommunication within said second subset of epochs in accordance with agradual decrease characteristic of said gradual decay policy.
 8. Amethod as claimed in claim 1 wherein said subset of epochs is a firstsubset of epochs, and said method further comprises: determining apriority characteristic of said network traffic; adjusting said firstsubset of epochs to form a second subset of epochs within said timewindow in response to said priority characteristic; communicating asecond message between said nodes in said network, said second messageidentifying said second subset of epochs as being allowable for use intransmitting said network traffic; and following receipt of said secondmessage, each of said nodes modifying said transmit capability mode byenabling communication of said network traffic during said second subsetof epochs and entering said idle state during said remaining ones ofsaid epochs.
 9. A method as claimed in claim 8 wherein: when saidpriority characteristic of said network traffic is greater than a highpriority threshold, increasing a second quantity of said epochs withinsaid second subset of epochs relative to a first quantity of said epochswithin said first subset of epochs for communication of said networktraffic; and when said priority characteristic of said network trafficis less than a low priority threshold, decreasing said second quantityof said epochs within said second subset of epochs relative to saidfirst quantity of said epochs within said first subset of epochs forcommunication of said network traffic.
 10. A method as claimed in claim8 wherein said priority characteristic is a latency characteristic ofsaid network traffic, and said method further comprises: determiningthat said latency characteristic calls for minimal latency intransmission of said network traffic; and increasing a second quantityof said epochs in said second subset of epochs relative to a firstquantity of said epochs within said first subset of epochs forcommunication of said network traffic.
 11. A method as claimed in claim1 wherein said selecting operations comprises selecting at least two ofsaid epochs within said time window for inclusion in said subset ofepochs, said at least two of said epochs being immediately adjacent oneanother within said time window of said epochs.
 12. A method as claimedin claim 1 wherein said selecting operations comprises selecting atleast two of said epochs within said time window for inclusion in saidsubset of epochs, said at least two of said epochs being approximatelyuniformly distributed within said time window of said epochs.
 13. Amethod as claimed in claim 1 wherein said one of said nodes is a networkmanager, and said monitoring, selecting and communicating operations areperformed by said network manager.
 14. A method as claimed in claim 1wherein said monitoring and selecting operations are performed by saideach of said nodes, and said communicating operation comprises:communicating a plurality of management messages between said nodes,said plurality of management messages including nodal traffic loads; andsaid selecting operation comprises collectively selecting said subset ofepochs for communication of said network traffic in response to saidnodal traffic load, said collectively selecting being performed bycommon consent between said nodes within said ad hoc network.
 15. Awireless ad hoc network comprising: a plurality of wireless nodesconfigured for network communication, each of said wireless nodes beingcapable of functioning in either of an operational mode and a sleepmode, wherein said operational mode includes a run state and an idlestate, said each wireless node consuming less power in said idle statethan in said run state; a processor for managing power consumption ofsaid nodes in said wireless ad hoc network; and a computer-readablestorage medium containing executable code for instructing said processorto perform operations comprising: monitoring a current traffic load ofsaid wireless ad hoc network; in response to said current traffic load,selecting a subset of epochs within a time window of epochs for networkcommunication; communicating a message between said nodes in saidnetwork, said message identifying said subset of epochs as beingallowable for use in communicating network traffic, wherein followingreceipt of said message, said each of said nodes modifies its transmitcapability mode by entering said run state to enable communication ofsaid network traffic over said network during said epochs within saidsubset of epochs and by entering said idle state during remaining onesof said epochs within said time window.
 16. A wireless ad hoc network asclaimed in claim 15 wherein said current traffic load is a first trafficload determined at a first instant in time, said subset of epochs is afirst subset of epochs, and said executable code instructs saidprocessor to perform further operations comprising: detecting a secondcurrent traffic load at a second instant in time following said firstinstant in time; adjusting said first subset of epochs to form a secondsubset of epochs within said time window in response to said secondcurrent traffic load; communicating a second message between said nodesin said network, said second message identifying said second subset ofepochs as being allowable for use in communicating said network traffic;and following receipt of said second message, said each of said nodesmodifying said transmit capability mode by entering said run state toenable communication of said network traffic during said epochs withinsaid second subset of epochs and by entering said idle state during saidremaining ones of said epochs within said time window.
 17. A wireless adhoc network as claimed in claim 15 wherein said processor and saidexecutable code are incorporated in each of said nodes, and saidexecutable code instructs said processor at said each node to performfurther operations comprising: communicating a plurality of managementmessages between said nodes, said plurality of management messagesincluding nodal traffic loads; and said selecting operation comprisescollectively selecting said subset of nodes for communication of saidnetwork traffic in response to said nodal traffic load, saidcollectively selecting being performed by common consent between saidnodes within said wireless ad hoc network.
 18. A method of powermanagement in a wireless ad hoc network, said network including aplurality of nodes, and said method comprising: monitoring a firsttraffic load of said wireless ad hoc network at a first instant in time;in response to said first traffic load, selecting a first subset ofepochs within a time window of epochs for network communication;communicating a message between said nodes in said network, said messageidentifying said first subset of epochs as being allowable for use incommunicating network traffic; following receipt of said message, saideach of said nodes modifying a transmit capability mode by entering arun state to enable communication of said network traffic over saidnetwork during said epochs within said first subset of epochs and byentering an idle state during remaining ones of said epochs within saidtime window; detecting a second traffic load and a prioritycharacteristic of said network traffic at a second instant in timefollowing said first instant in time; adjusting said first subset ofepochs to form a second subset of epochs within said time window inresponse to said second current traffic load and said prioritycharacteristic; communicating a second message between said nodes insaid network, said second message identifying said second subset ofepochs as being allowable for use in communicating said network traffic;and following receipt of said second message, said each of said nodesmodifying said transmit capability mode by entering said run state toenable communication of said network traffic during said epochs withinsaid second subset of epochs and by entering said idle state during saidremaining ones of said epochs within said time window.
 19. A method asclaimed in claim 18 further comprising comparing said second currenttraffic load with one of a high traffic load threshold and a low trafficload threshold; said adjusting operation increases a second quantity ofsaid epochs within said second subset of epochs relative to a firstquantity of said epochs within said first subset of epochs when saidsecond current traffic load is greater than said high traffic loadthreshold; and said adjusting operation decreases said second quantityof said epochs within said second subset of epochs relative to saidfirst quantity of said epochs within said first subset of epochs whensaid second current traffic load is less than said low traffic loadthreshold.
 20. A method as claimed in claim 18 wherein said prioritycharacteristic is a latency characteristic of said network traffic, andsaid method further comprises: determining that said latencycharacteristic calls for minimal latency in transmission of said networktraffic; and increasing a second quantity of said epochs in said secondsubset of epochs relative to a first quantity of said epochs within saidfirst subset of epochs for communication of said network traffic.